Trevor,
Use Unevaluated.
f[n_] :=
Switch[n,
1, "foo",
2, Unevaluated[Sequence[ ]],
3, {"bar"}];
f /@ {1, 2, 3}
{foo, {bar}}
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Trevor Baca [mailto:trevorbaca at gmail.com]
To: mathgroup at smc.vnet.net
What's the right way to have an expression evaluate to an empty
sequence?
I'd like ...
f[n_] :=
Switch[n,
1, "foo",
2, Sequence[ ],
3, {"bar"}];
... to work, but instead I get the message
Switch::"argct": "Switch called with 6 arguments. Switch must be called
with an odd number of arguments."
meaning that the Sequence[ ] is flattened in the rhs definition of f[
].
Is there a way to get f[ ] to evaluate to the empty Sequence[ ] (rather
than Null)?
Trevor.